The present invention relates to a shuttle type line printer in which a hammer bank unit having a plurality of printing hammers mounted widthwise of paper and a counter balancer unit are separately reciprocated in opposite directions to perform printing.
A conventional shuttle type line printer in constructed as shown in Japanese Laid-Open Patent No. 288657/1991 and FIG. 1. The conventional shuttle type line printer shown in FIG. 1 will be first described for better understanding, and the construction thereof is as follows.
In FIG. 1, reference numeral 1 designates a hammer bank provided with a plurality of printing hammers along printing lines 1' designates a hammer bank mounting bed; element 2 is a yoke and counter balancer provided with solenoid coils 3-1 and 3-2. This counter balancer 2 is provided parallel with the hammer bank mounting bed 1' and is connected to a connection belt 5 extended over rotary drums 4-1 and 4-2 provided on the opposite sides so that they are oscillated in opposite directions.
The solenoid coils 3-1 and 3-2 stand face to face with permanent magnets 6-1 and 6-2 secured to a frame (not shown) to constitute a linear motor, and a current is allowed to flow into the solenoid coils in the reverse direction at fixed intervals so that the counter balancer 2 and the hammer bank 1 are oscillated in opposite directions.
Reference numerals 7-1 to 7-4 respectively designate repulsion stoppers provided on opposite sides in order to minimize a motor thrust required for deceleration at the end of the oscillation strokes of the hammer bank 1 and the counter balancer 2. Reference numeral 8 designates a platen. It is to be noted that the repulsion stoppers in FIG. 1 are schematically shown, and are actually formed from rubber or a spring system such as a spring.
In the conventional hammer bank oscillation apparatus shown in FIG. 1, both the hammer bank mounting bed 1' and the counter balancer 2 simultaneously collide with repulsion springs opposite to left and right from each other at the end of the shuttle operation. However, since they are connected by the connection belt 5, a force couple F.times.2 L, which is expressed by the product between a force F caused by the collision and a distance 2 L between axes of the hammer bank mounting bed 1' and the counter balancer 2, occurs to produce an impact force by which the hammer bank mounting bed 1' is rotated, resulting in the cause of vibrations which brings forth the lowering of the printing dot accuracy. Further, since the connection belt 5 is used to connect the hammer bank mounting bed 1' and the counter balancer 2, the part accuracy and the assembly accuracy required to secure the reliability of the connection belt 5 are very high, adversely affecting the cost. In addition, the low strength of the connection belt 5 impedes the realization of higher speed.
On the other hand, for the purpose of attaining a high-speed printing of a printer, there is a system in which printing hammers mounted on the hammer bank are provided in a multi-stage fashion in a direction of feeding paper to be printed as shown in FIG. 2. In the case where this system is used, the reciprocating amount of a shuttle mechanism (a mechanism for reciprocating a hammer bank unit and a counter balancer unit) in a direction widthwise of the paper increases. Morover, it is preferred that an area for printing to be effected is uniform in order to improve the quality of printing.
In the construction shown in FIG. 1, however, the hammer bank unit and the counter balance unit are connected by the connection belt. Therefore, it has been difficult to increase the reciprocation amount of the hammer bank in the direction widthwise of the paper and to make the printing area uniform.